World energy investment has been greatly in demand of the development of clean energy and more efficient energy system, in order to reduce energy loss and lower CO2 emissions. Since the heat transfer is the key to the energy conversion, for decades, many researchers have been taking great effort on the research and development for an enhanced heat transfer as well as a more efficient heat and mass transfer. The heat pipe invented in 1960s has been one of major breakthroughs in heat industry. This heat pipe technology brings new challenges and opportunities to current thermal technology and engineering, via heat transfer mode and heat transfer material, which is in particular brought by the nanotechnology.
In 1995, Choi et al in Argonne National Laboratory proposed a new concept—nanofluid, which is a particle suspension that consists of base liquids and nano-sized metallic/metal oxide particles, and has great potential for heat transfer enhancement because of its nanoscale effect. When the nanoparticle radius is smaller than, or similar to the heat-carrier mean free path of the host medium, the heat transfer could be nonlocal and nonlinear. Thus, the particle temperature rise is much larger than the prediction of the Fourier conduction theory. Besides, the micro convection caused by the Brownian movement of nanoparticles, congregation of nanoparticles, and orderly array of liquid molecules at the interface between the nanoparticle surface and the base fluid, contribute to the heat transfer of nanofluid. Therefore, many efforts have been on the manipulation of a nanofluid to achieve the desired heat transfer performance. However, the nanofluid as a heat transfer medium, is hard to applicable to high temperature and high pressure apparatus, and achieve the isothermal heat transfer. Previous reports show some common issues, such as: (1) large amounts of hazardous substances, which is not in compliance of international environmental standards; (2) low melting point, leading a narrow working temperature range; (3) dynamic corrosion inhibition issue, causing the ageing of thermal transfer devices and reducing the heat transfer efficiency; (4) to solve the particle congregation issue, some even tried to consider the radioactive hazardous substances; (5) the stability of thermal transfer fluid; the metal particles in the thermal fluid are easily oxidized; (6) limited heat transfer ability in the radial direction; and (7) difficulty to be applicable in high temperature and high pressure apparatus.
Prior heat transfer mediums have also included products comprising layers to provide combinations of components such as described in U.S. Pat. No. 6,132,823 to Qu. US Patent Publication 2005/0179001 describes heat-transfer mediums having an aqueous solution of one or more kinds of salts, including metallic ions. U.S. Pat. No. 7,919,184 to Mohaptra et al describes heat transfer materials comprised of hybrid nano-particles that comprise a phase change materials (PCM) (such as a wax) encapsulated in a metal layer.
PerformanceNanoparticleSize (nm)FluidVol % in fluidknf/kfReferenceMetal oxidesAl2O3 60.4H2O 5.01.23Xie, JMSl, 2002, 21, 1469-1471CuO 23H2O 4.5-9.7 1.17-1.34Wang, JTHT, 1999, 13, 474-480Fe3O4 6.7H2O 6.33Philip, AIP, 2007, 91, 213108ZnO 29 & 77EG/H2O 71.485 (@ 363K)Vajjah, UHMT, 2009, 52, 4675(60/40)CeO2 74H2O 41.19Beck, JAP, 107, 066101ZrO2H2O 1.32 1.02-1.03Rea, UHMT, 2009, 52, 2042Other oxides andAlN (withtransformer 0.51.08Choi,CurrAppl Phys 2008;8:710Nitride/carbideAl2O3)oilceramicsSiC170H2O 7 1.28Singh, J Appl Phys2009;105:064306 90EG/H2O 41.16Timofeeva, JAP, 2011;109:014914(50/50)SiO2H2O?311.18Shalkevich, J. Phys. Chem. C,2010, 114, 9568 1523.31.144 (@ pH = 10.1)Wu, Phys Rev E2010;81:011406SemiconductorsTiO210 × 40(rod)/H2Oup to 51.33/1.30Murshed, Int J ThermSci15 (sph)2005;44:367 25H2O 11.14Yoo, ThermochimActa 2007;455:66SnO2 1H2O 0.024 (wt %)1.087 (pH = 8)Habibzadeh, ChemEng J2010;156:471MetalsAl 20H2O  1-51.035-1.23Xuan, UHFF, 200, 21, 58Ag  8-15H2O0.10-0.39 1.03-1.11Kang, Exp. Heat Transfer.2006, 19, 181Au 40H2O 0.111.014Shalkevich, Langmuir, 2010, 26, 663Cu 10-20H2O 0.000131.03Patel, Appl Phys Lett2003;83:2931 50-100H2O 0.101.24Liu, UHMT,2006, 99, 084308Fe 20H2O 1.0-3.0 1.12-1.29Xuan, UHFF, 2000, 21, 58 10EG0.20-0.55 1.13-1.18Hong, JAP, 2005, 97, 064311CNTsM-CNTs130 (Φ),H2O 0.601.34Assael, IntJ Thermophyslength >2005;26:64710000 20-50 (Φ)EG 1.001.124Liu, IntCommu Heat Mass Transfer2005;32:1202S-CNTs0.8-1.6H2O 0.3 1.16 (@ 333K)Harish, Materials Express, 2012, 2, 213Graphene andGNEG 51.86Yu, Phys Lett A 2011;375:1323graphene oxideH2O 0.056 1.14 (25° C.)Baby, J Appl Phys 2010;108:124308nanosheets 1.64 (50° C.)GONEG 51.61Yu, Phys Lett A 2011;375:1323
Prior heat transfer mediums also often contain environmentally hazardous materials, such as chromium or compounds containing chromium.
Heat pipes are widely used to provide heat transfer to effect cooling in many applications, ranging from consumer electronics to electric power generating plants. Such heat pipes typically contain a heat transfer fluid or medium. Examples of such heat transfer fluids/mediums include water, alcohols, refrigerants (such as Freon), ammonia, and mixtures thereof. But such materials typically do not provide heat transfer effectiveness over a broad range of operating temperatures. In addition, some heat transfer mediums are corrosive to the heat pipes.
The present invention provides heat transfer mediums that provide superior heat transfer characteristics, while also avoiding the drawbacks of prior mediums.